Such a refrigerant compressor is, for example, known from GB 1,122,348. This refrigerant compressor has in one embodiment three cylinders arranged in a star-shape. The pistons arranged in the cylinders are driven to a reciprocating movement by the crankshaft via a common crank pin. An oil pump arrangement is formed by an inclined pipe, whose end is submerged in the oil sump.
Such a refrigerant compressor serves the purpose of compressing refrigerant that is available in a gaseous form. This will cause a substantial load in the bearings, which connect mutually moving parts to one another. This is particularly the case, if refrigerants are used, which require a higher pressure, for example environmentally friendly refrigerants, such as CO2.
Therefore, practically all refrigerant compressors use a lubrication, in which oil from the oil sump is supplied to certain places in order to reduce friction between mutually moving parts and thus also to reduce the wear.
For an energy saving mode of operation of a refrigerant compressor, it may be necessary to drive the refrigerant compressor with variable speed. In this case, it may be difficult always to ensure the oil supply. For example in connection with low speeds and the use of a centrifugal pump, only low pressures occur, with which the lubricant supply to the corresponding bearing points cannot always be ensured. With high speeds, however, the oil pressures are high, so that excess oil will be sprayed inside the housing. This involves the risk that oil will be mixed with the refrigerant, which is also supplied via the inside of the housing.
Another possibility is to build up a pressure difference between the oil sump and the bearing points, for example by means of a displacement pump. This, however, also involves the risk of generating a large oil flow, which will cause a relatively large leakage of the oil into the refrigerant flow. A narrowing of the channels carrying oil, to reduce the oil flow, can cause other problems, for example choking channels and relatively low flow rates of the oil at low speeds.